Arrangement for saving energy in transmitter

ABSTRACT

An arrangement for saving energy in a radio device transmitter and a radio device. The steady currents of the transmitter amplifiers are made dependent on the transmitting power for reducing the losses of the amplifiers. The VGA ( 400 ) comprises at least one main differential pair (Q 41 –Q 42 ; Q 43 –Q 44 ) for controlling the gain and a bias differential pair (Q 47 –Q 48 ) for controlling said steady currents. These pairs are steered by the one and the same voltage (ΔV), in which case the output current (I b1 ; I b2 ) of the bias differential pair changes in the same way as the output current (i o1 ; i o2 ) of the main differential pair when the gain is readjusted. The output current of the bias differential pair is used as a bias current of the transmitter amplifiers, i.e. as a current that determines the steady currents of the amplifiers. Because the values of the steady currents of the amplifiers track accurately the value of the gain, when this is changed, the steady currents are always so low as the transmitting power necessarily requires, at a given time, wherein the amount of needless losses, from the transmitting operation&#39;s point of view, is small. Said differential pairs are placed on one and the same substrate, in order to the control to function accurately in a wide dynamic range.

The invention relates to an arrangement for saving energy in a radiodevice transmitter by means of controlling current consumption. Theinvention also relates to a radio device having an arrangement accordingto it.

BACKGROUND OF THE INVENTION

Small-sized portable radio devices, as mobile phones, should consume solittle energy as possible to lengthen the use time of the battery and toavoid heating problems. Furnishing a phone with plurality of additionalactivities contributes to giving rise to energy saving. Most importantobjects, from the point of energy saving, are naturally those, whoseenergy consumption is relatively high. The radio frequency amplifiers ofthe transmitter are such objects, especially. Energy losses inevitablyoccur in the amplifiers. If the transmitting power of a transmitterwould be constant, it would be easy to design the amplifiers so that theenergy losses would be relatively low. However, in mobile terminals thetransmitting power is changeble, because it is intentionally tried to beset to a value that is just sufficient. Unnecessary high transmittingpowers cause rise of noise level in a radio network, which is avoided,of course. The power control range may be even 50 dB. The problem inthat case is keeping the dissipation power down when using lowtransmitting powers.

FIG. 1 shows an example of a radio transmitter as a block diagram and ofa principle, known as such, how to affect the dissipation power of theamplifiers. The transmitter comprises, listed in the propagationdirection of the signal to be transmitted, a modulator MOD, a variablegain amplifier VGA, a driver amplifier DRA, a matching filter MFI, apower amplifier PA, an antenna filter AFI of the transmitting side andan antenna ANT. Abbreviation VGA will be used for the said variable gainamplifier in this description as well as in the claims for briefness andclarity. The analogous converted parts I and Q of the signal to betransmitted and a carrier LO are led to the quadrature type modulatorfrom a local oscillator. The VGA is joined to the bus of the radiodevice, through which bus the gain of the VGA and thus the transmittingpower of the whole transmitter are set programmably. The power amplifierPA has a separate driver amplifier DRA, because placing the driveramplifier in the same integrated circuit with the power amplifier wouldresult in temperature problems in the driver amplifier. The output powerof the driver amplifier is already remarkably high, and should thus betaken into account in the energy saving arrangements.

The dissipation powers of the driver and power amplifiers are affectedthrough their steady currents in FIG. 1. When the input signal level ofthe driver amplifier is at its height, the steady currents must be highenough so that it is possible to rise the output power of the poweramplifier to a specified maximum value. When the level of the inputsignal lowers from its maximum value, the steady currents can beunchanged from the output power's point of view. However, in principlethis means unnecessary losses inside the amplifiers. By lowering thesteady currents these losses are reduced at the same time, because theproducts of the current and voltage of the internal components of anamplifier are reduced. The lower the level of the input signal is, themore there is room for decreasing the steady currents. The output powerof the transmitter is determined by the gain of the VGA, as mentionedabove. The VGA then indirectly has information about the transmittingpower. This matter is utilized by including a bias current source 130 ofthe driver and power amplifiers into the VGA, the input signal of whichsource is the same as the gain control voltage set through the bus. Whenthe gain is increasing, a bias current I_(bias) becomes higher and viceversa. Both the driver amplifier DRA and the power amplifier PA have abias current of their own, which bias current determines the steadycurrent in the amplifier.

FIG. 2 shows an example of variable gain amplifier VGA, including aknown bias current source. The VGA 200 comprises an amplifier proper210, control circuit 220 thereof and a bias current source 230. Theamplifier proper 210 has a bipolar differential pair Q21–Q22. Theemitters of these transistors are connected to a controllable signalcurrent source 211, the second current terminal of which being connectedto the ground. The collector of the first transistor Q21 is directlyconnected to the supply voltage V_(s) and the collector of the secondtransistor Q22 is connected to a driver amplifier DRA, which is notshown in FIG. 2. When the base currents of the transistors are not takeninto account, the current i_(in) of the current source 211 is the sum ofthe first collector current i₁ and the second collector current i_(out).The signal current source 211 is controlled by the input signal v_(in)of the amplifier. The second collector current i_(out) is at the sametime the output signal of the amplifier. The base of the firsttransistor Q21 is connected to a reference voltage V_(r1) through aresistor R21 and the base of the second transistor Q22 is connected tothe output of the control circuit 220 through a resistor R22.

The control circuit 220 comprises an operational amplifier A21, afeedback resistor R23 thereof and a second controllable current source221. The non-inverting input of the operational amplifier is connectedto a reference voltage V_(r2) and the current source 221 is connectedfrom the inverting input to the ground. The current source is controlledexternally by the gain control signal V_(G). The direction of the sourcecurrent I_(GT) is towards the ground, in which case the output voltageof the control circuit V_(GT)=V_(r2)+R23·I_(GT)=V_(r2)+aV_(G), where ais a constant. When the output voltage of the control circuit isenhanced by the control signal V_(G), the current i_(out) of the secondtransistor is enhanced and the current i₁ of the first transistor isreduced the same amount. The current i_(in) remains unchanged, whereuponthe current gain G_(I) becomes greater. The maximum value of the currentgain is one, in which case the current i_(in) of the current source 221flows wholly through the second transistor Q22. By means of the controlcircuit also a temperature compensation of the gain can be implemented.

The bias current source 230 comprises an operational amplifier A22, tothe non-inverting input of which the above-mentioned gain controlvoltage V_(G) is fed. The output of the operational amplifier isconnected to the gate of a n-channel fet Qb, and the source of the fetQb is connected to the signal ground through a resistor R24. From thesource of the fet there is also a feedback to the inverting input of theoperational amplifier, which feedback forces the voltage over theresistor being equal to the control voltage V_(G). Thus the currentI_(D) flowing in the channel of the fet is equal to V_(G)/R24. The drainof the fet Qb is connected to the output of the bias current source 230.Prerequisite of the fet current naturally is that the output isconnected to the supply voltage through some way. Between the sameoutput and the ground there is further connected a constant currentsource 231, the current of which is I_(co). The output current, or thebias current I_(bias), then is the sum of the currents I_(D) and I_(co).In FIG. 2 occurs only one bias current. The bias current is dividedbetween the driver and power amplifiers or it controls a circuit thatproduces two bias currents. The current I_(co) is relatively low and itsecures that the bias current never drops quite close to the zero. Avery low bias current would cause the amplifier to change unstable.

In this description the reference “R” means both a resistance and aresistor (component), the resistance of which is R. The term“differential pair” refers in this description and in the claims to twotransistors, the emitters of which are connected together. The totalemitter current is then divided between the transistors in a certainratio depending on the control led to the bases.

A flaw of the above-described arrangement is, that the control of thelosses of the driver amplifier and power amplifier is far from anoptimal control. This is due to the fact that the bias current'sdependence on the transmitter gain is very non-linear. Let us suppose anexemplary situation, that the transmitting power has to be dropped 40 dBfrom its maximum value. This corresponds to decreasing the current gainG_(I) to the hundredth part. In the VGA of FIG. 2 the decreasing of thecurrent gain to the hundredth part, from the value 0.99 to the value0.01, takes place when the control voltage V_(G) is lowered e.g. to thehalf, in which case the ratio of the control voltage is two. An accuratevalue depends on detailed implementation of the circuit, mainly on theselection of the reference voltages. In any case the ratio of thecontrol voltage is much smaller than the ratio of the gain. The biascurrent of the driver and power amplifiers and therefore also the steadycurrents of these amplifiers decrease about in the same ratio as thecontrol voltage V_(G). In the above-mentioned example the steadycurrents decrease to the half, altough there would be room for almostdouble decreasing, e.g. about to the hundredth parts of the originalvalues. Correspondingly one half of the losses of the amplifiers failsto cut.

SUMMARY OF THE INVENTION

An object of the invention is to reduce said disadvantage related to theprior art. An arrangement according to the invention is characterized inthat which is specified in the independent claim 1. A radio deviceaccording to the invention is characterized in that which is specifiedin the independent claim 8. Some preferred embodiments of the inventionare specified in the dependent claims.

The basic idea of the invention is as follows: The steady currents ofthe transmitter amplifiers are made dependent on the transmitting powerfor reducing the losses of said amplifiers. The VGA comprises at leastone main differential pair for controlling the gain and a biasdifferential pair for controlling said steady currents. These pairs aresteered by the one and the same voltage, in which case the outputcurrent of the bias differential pair changes in the same way as theoutput current of the main differential pair when the gain isreadjusted. The output current of the bias differential pair is used asa bias current of the transmitter amplifiers, e.g. as a current, whichdetermines the steady currents of the amplifiers. Said differentialpairs are placed on one and the same substrate.

An advantage of the invention is that needless losses, from thetransmitting operation point of view, are avoided better than in theknown transmitter structures. This is due to that the values of thesteady currents of the amplifiers track accurately the value of thegain, when the gain is changed. Thus the steady currents are always aslow as the transmitting power necessarily presumes, at a given time.Another advantage of the invention is that the prevention of needlesslosses functions accurately also when the dynamics of the amplifiers iswide, i.e. when the control range of the gain is large. This is due tothat the bias differential pair controlling the steady currents and themain differential pair/pairs are accurately similar functionally,because they are formed in one and the same manufacturing process on oneand the same substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail. Reference will be made tothe accompanying drawings wherein

FIG. 1 presents a transmitter of a radio device as a block diagram,

FIG. 2 presents an example of a VGA in accordance with the prior artwith a bias current source for the transmitter amplifiers,

FIG. 3 presents an example of a VGA in accordance with the inventionwith a bias current source for the transmitter amplifiers,

FIG. 4 presents another example of a VGA in accordance with theinvention with a bias current source for the transmitter amplifiers,

FIG. 5 presents an example of a radio device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows an example of a VGA according to the invention, having abias current source for the transmitter amplifiers. The VGA 300comprises an amplifier proper 310, control circuit 320 thereof and thebias current source 330. The amplifier proper 310 is substantiallysimilar to the amplifier 210 in FIG. 2. It has a bipolar maindifferential pair Q31–Q32, the emitters of which are connected to asignal current source 311 controlled by the input signal v_(in) of theamplifier. The output signal of the amplifier is the collector currenti_(out) of the second transistor Q32. The current gain G_(I) of theamplifier is i_(out)/i_(in), where i_(in) is the current of the source311, or the total current of the amplifier 310. The base of the firsttransistor Q31 is connected to a reference voltage V_(r1) and the baseof the second transistor Q32 is connected to the output of the controlcircuit 320.

The control circuit 320 is similar to the control circuit 220 in FIG. 2.When the input voltage of the control circuit 320, or the gain controlvoltage V_(G), is raised, the output voltage V_(GT) of the controlcircuit rises, whereupon also the current gain G_(I) becomes greater. Ifthe second reference voltage V_(r2) has been chosen suitably, thecurrent gain can be adjusted almost in the range 0 . . . 1.

The bias current source 330 comprises a differential pair Q33–Q34, theemitters of which are connected to a constant current source 331. Thebase of the transistor Q33 is connected to a reference voltage V_(r1)and the base of the second transistor Q34 is connected to the output ofthe control circuit 320. The differential pairs Q31–Q32 and Q33–Q34 thenare connected parallel so that they get the same steering. In that casethe collector current I_(u) of the transistor Q34 changes in proportionas the output current i_(out) of the amplifier proper 310 and thecurrent gain G_(I) when the gain is readjusted. As said differentialpairs are manufactured in one and the same process on one and the samesubstrate, a change in current I_(u) tracks the change in the currentgain very accurately. The accuracy is necessary, if the gain controlrange is dozens of desibels.

The load of the transistor Q34 is a MOSFET (Metal Oxide SemiconductorField Effect Transistor) type transistor M31. The bias current source330 further comprises a second M32 and third M33 MOSFET, each of whichforms a so called current mirror circuit with the MOSFET M31. This meansthat the ratio of both the current I_(bi1) of the second MOSFET M32 andthe current I_(bi2) of the third MOSFET M33 to the collector currentI_(u) of the transistor Q34 remains unchanged. The current I_(bi1) isused as the bias current of the driver amplifier DRA and the currentI_(bi2) is used as the bias current of the power amplifier PA. FIG. 3shows an example of the control of the steady current, for the part ofthe power amplifier. For the control the power amplifier comprises acurrent mirror circuit formed by MOSFETs M34 and M35. The bias currentI_(bi2) is led through the directing MOSFET M34 in the current mirror,whereupon the ratio of current I_(dc) of the MOSFET M35 to the biascurrent I_(bi2) remains unchanged. The current I_(dc) is used as thesteady current of the power amplifier PA. The current mirror is madeasymmetric so that the bias current I_(bi2) is substantially lower thanthe steady current I_(dc), for instance a tenth part of the steadycurrent. In that way the internal currents of the bias current source330 are made low and the energy consumption caused by the bias currentsource to be low compared with the energy saving obtained by means ofthe invention. A low constant current I_(k) is added to the bias currentI_(bi2) in the power amplifier, that the steady current I_(dc) shouldnever get too close to zero.

FIG. 4 shows another example of a VGA according to the invention, havinga bias current source for the transmitter amplifiers. Also the VGA 400comprises an amplifier proper 410, control circuit 420 thereof and thebias current source 430. The amplifier proper 410 is in this examplefully differential. It has three differential pairs. The first pairformed by transistors Q41 and Q42 and the second pair formed bytransistors Q43 and Q44 are connected parallel such that the bases ofthe transistors Q41 and Q43 are connected together as well as the basesof the transistors Q42 and Q44. The collectors of the transistors Q42and Q44 are connected directly to the supply voltage V_(s). Thecollectors of the transistors Q41 and Q43 are connected to a load, whichconsists of the input stage of the following amplifier. The collectorcurrent i₀₁ of the transistor Q41 and the collector current i_(o2) ofthe transistor Q43 are output quantities of the amplifier 410. They aredifferential: As the one collector current is increasing due to a changein the input signal v_(in) of the amplifier, the other collector currentis decreasing.

The third differential pair is formed by the transistors Q45 and Q46.The collector of the transistor Q45 is connected to the emitters of thefirst pair, thus the current i_(i1) of the transistor Q45 is the same asthe total current of the first pair. Correspondingly the collector ofthe transistor Q46 is connected to the emitters of the second pair, thusthe current i_(i2) of the transistor Q46 is the same as the totalcurrent of the second pair. The third pair is steered by the inputsignal v_(in) of the amplifier, which exists between the bases of thetransistors Q45 and Q46. A first steady current source 411 is connectedbetween the emitter of transistor Q45 and the ground, and a secondsteady current source 412 between the emitter of transistor Q46 and theground. A resistor R_(E) is connected between these emitters, whichresistor affects the base gain of the amplifier.

In FIG. 4 the control circuit 420 is presented only as a symbolic block.The gain control voltage V_(G) steers an amplifier circuit, which hasbalanced differential output. The first output terminal, the voltage ofwhich is V₁, is connected to the parallel bases of the transistors Q41and Q43. Correspondingly the second output terminal, the voltage ofwhich is V₂, is connected to the parallel bases of the transistors Q42and Q44. The voltage difference V₁−V₂=ΔV then controls the current gainin the amplifier 410.

The bias current source 430 is similar to the bias current source 330 inFIG. 3. It comprises a differential pair Q47–Q48, the emitters of whichare connected to a constant current source 431. The collector circuit ofthe transistor Q48 is similar current mirror circuit 435 to that theMOSFETs M31, M32 and M33 form in FIG. 3.

The circuit 435 outputs two bias currents I_(b1) and I_(b2), whichchange in proportion as the collector current of the transistor Q48. Thebase of the transistor Q47 is connected to the first output terminal ofthe control circuit and the base of the transistor Q48 is connected tothe second output terminal of the control circuit. The differential pairof the bias current source then is connected parallel to the first andsecond pairs of the amplifier proper 410 so that all three pairs get thesame steering ΔV. In that case the bias currents I_(b1) and I_(b2)change in proportion as the output currents i_(o1) and i_(o2) of theamplifier proper and the current gain when this is read-justed. As saiddifferential pairs are manufactured in one and the same process on oneand the same substrate, changes in bias currents track also in this casethe change in the current gain very accurately. The bias currentscontrol the steady current of the transmitter power amplifier and of thedriver amplifier of the power amplifier. The bias currents as such arealso in this case remarkably lower than the steady currents at issue foravoiding losses in the bias current source 430.

FIG. 5 shows an example of a radio device according to the invention.The radio device RD comprises a VGA 500 and an arrangement according tothe invention, for saving energy.

Amplifier according to the invention is described above. The inventionis not limited only to the depicted structures; the circuit solutionscan vary widely. The current saving may be applied also on the VGAitself in addition to the driver and power amplifiers, with the sameprinciple. The inventional idea can be applied in different ways withinthe scope defined by the independent claim 1.

1. An arrangement for saving energy in a radio device transmitter, radiofrequency amplifiers of which being at least a VGA and a poweramplifier, which VGA comprises at least one main differential pair,total current of which being arranged to be dependent on input signal ofthe VGA and a collector current of one transistor of the maindifferential pair being output signal of the VGA, the VGA furthercomprising a control circuit to change mutual steering of transistors inthe main differential pair so that VGA's current gain changescorresponding to changes in a gain control signal, the arrangementcomprising in the VGA a bias current source controllable by said gaincontrol signal, output of which bias current source being connected tosaid power amplifier to make a steady current of the power amplifierdependent on the current gain and thus transmitting power, wherein; saidbias current source comprises a bias differential pair, the bases of thetransistors of which are connected parallel to the bases of thetransistors of the main differential pair for steering these pairs byone and the same control signal, and a current of said output of thebias current source is arranged to track in proportion collector currentof the transistor of the bias current source, the base of which isparallel with the base of said one transistor of the main differentialpair.
 2. The arrangement according to claim 1, the bias differentialpair and the main differential pair being located on one and the samesubstrate to equalize the electric characteristics of these pairs. 3.The arrangement according to claim 1, output current of the bias currentsource being arranged to track in proportion the collector current ofthe transistor of the bias differential pair by means of a currentmirror circuit, a transistor of which is load of said transistor of thebias differential pair and a current of another transistor of thecurrent mirror circuit is output current of the bias current source. 4.The arrangement according to claim 1, the steady current of the poweramplifier being arranged to track in proportion the output current ofthe bias current source by means of a second current mirror circuit, atransistor of which is load of said output of the bias current sourceand a current of another transistor of the second current mirror circuitis the steady current of the power amplifier.
 5. The arrangementaccording to claim 4, said second current mirror being asymmetric sothat the output current of the bias current source is substantiallylower than the steady current of the power amplifier to reduce the ownlosses of the bias current source.
 6. The arrangement according to claim1, the radio device transmitter further comprising a driver amplifierfor said power amplifier, wherein; the bias current source further has asecond output, a current of which is arranged to track in proportion thecollector current of the transistor of the bias differential pair, thebase of which is parallel with the base of said one transistor of themain differential pair, which second output is connected to said driveramplifier to make a steady current of the driver amplifier dependent onthe current gain and thus transmitting power.
 7. The arrangementaccording to claim 1, the control circuit of the VGA having adifferential output, wherein; the VGA comprises first and second maindifferential pairs being parallel such that the bases of firsttransistors of these pairs are connected to first terminal of thedifferential output of the control circuit and the bases of secondtransistors of these pairs are connected to second terminal of thedifferential output of the control circuit, and said input signal isarranged to be fed to a third differential pair, the collector of firsttransistor of the third pair being connected to the emitters of thetransistors of the first pair and the collector of second transistor ofthe third pair being connected to the emitters of the transistors of thesecond pair.
 8. A radio device comprising the arrangement as in claim 1.